18 mos of what? If you mean i-131 for graves' disease that you've had for 18 mod., it would probably be very effective. What have you been doing to treat your thyroid problem for the past 18 months? Hopefully not letting it go untreated. I-131 is effective 95-98% of the time, but can lead to hypothyroidism, although that is very easy to manage.
Have thyroid checked. Rai can make someone with hyperthyroidism hypothyroid and so you will need replacement to bring the thyroid values into normal range. Sometimes this is the way to go if oral medication cannot control the hyperthyroidism.
Hashitoxicosis. I am presuming you are hyperthyroid, but there is evidence of thyroid inflammation, or high tpo antibodies. If the thyroid is tender, nsaids or possibly Prednisone is used. Most endocrinologists would treat the hyperthyroidism with meds (methimazole, beta blockers) and then recommend either radioactive iodine or surgery. Read more...